376 



UNITED STATES MINERAL RESOURCES 



very rich lenticular unit on the hanging-wall side 

 of the pegmatite, generally well removed from the 

 lepidolite core and surrounded by a spodumene-rich 

 intermediate zone containing petalite (Cooper, 1964, 

 p. 450-451 and figs. 3, 6, and 7; Martin, 1964, p. 

 124 and pi. 8; Hutchinson, 1959, p. 1534 and figs. 

 2 and 5 ; Wright, 1963, p. 936 and pi. 1 ; Grouse and 

 Cern^, 1972, figs. 3 and 4). 



PRODUCTION 



Production and consumption figures for cesium 

 are rarely published. Howe and Rovratree (1966, p. 

 211) say that the United States in 1964 used about 

 8 short tons of cesium salts and somewhat more 

 than 3,000 pounds of cesium metal. In 1970, the 

 United States imported 5,129 pounds of cesium com- 

 pounds plus an unstated quantity of pollucite, and 

 the U.S.S.R. imported 200 tons of pollucite contain- 

 ing about 40 tons of cesium (Kurtz, 1972). From 

 these figures, the world's consumption now and in 

 the immediate future may be gaged at only a few 

 tons of cesium annually. Prices are high; the 5,129 

 pounds of cesium products imported in 1970 were 

 valued at $189,056 (Kurtz, 1972), or about $37 

 per pound. 



The principal source has been the Bikita pegma- 

 tite, mainly from pollucite but also as a byproduct 

 of the extraction of lithium from lepidolite, which 

 resulted in an alkali carbonate residue containing 

 about 2 percent cesium. South West Africa has been 

 the other source in recent years, and Mozambique 

 has also yielded cesium (Howe and Rowntree, 1966, 

 p. 211). Only about 100 tons of pollucite has been 

 mined in the United States, mostly from the Tin 

 Mountain pegmatite. Black Hills, S. Dak., but also 

 from Oxford County, Maine. All these sources are 

 likely to be dwarfed by the Tanco deposit during 

 any expansion of the cesium market unless a now 

 unanticipated source of cesium (for example, as a 

 byproduct of brine processing) makes an appear- 

 ance. 



RESERVES AND RESOURCES 



Reserves of the Tanco deposit have most recently 

 been placed at 293,863 tons of pollucite with 23.67 

 percent CsaO, or 66,000 tons of cesium (Mining 

 Engineering, April 1962, p. 18). At Bikita the di- 

 mensions of the pollucite body, as furnished by 

 Martin (1964, p. 124 and pi. 8), imply about 25,000 

 tons of cesium. Reserves in South West Africa may 

 also be sizable, but elsewhere in the world the known 

 amount of pollucite is negligible. Nevertheless, the 

 world's total reserves may be placed at very close 

 to 100,000 tons of cesium, which is virtually infinite 



relative to the trivial annual consumption or to 

 anticipated demand. 



Estimates of conditional or hypothetical resources 

 are not worthwhile in the absence of data and in 

 the absence of any predictable need for a larger 

 quantity of cesium. If one makes the plausible as- 

 sumption that the ratio between cesium reserves 

 and proved and probable reserves of lithium in peg- 

 matites (about 1:7) will remain approximately the 

 same as additional lithium deposits are developed, 

 the world has resources of several hundred thousand 

 tons of cesium. 



RUBIDIUM 



Rubidium resources cannot be appraised in the 

 same way as lithium or cesium resources because no 

 rubidium minerals or rubidium-rich waters have 

 been found or seem likely to be found, and all ru- 

 bidium recovered is byproduct. The amount of 

 rubidium available suffices for the small demand, 

 and probably other byproduct sources could be 

 tapped to increase the supply without much effect 

 on prices. 



Consumption figures for rubidium are unpublished 

 but apparently are even smaller than for cesium, 

 which in some uses serves the same purpose as 

 rubidium. Consumption is mainly in research and 

 development, but rubidium is also used in vacuum 

 tubes, photocells, and medicine (Heindl, 1970, p. 

 700-702). The main source in recent years has been 

 the alkali carbonate residue of the lepidolite plant 

 formerly at San Antonio, Tex., the stock of v/hich 

 has not yet been exhausted, but it is also a byprod- 

 uct of the processing of pollucite (Heindl, 1970, p. 

 700). 



The apparent absence of independent rubidium 

 minerals is attributable to chemical properties which 

 enable rubidium to substitute for potassium, a 

 ubiquitous constituent not only of granites and clays, 

 which have the highest average contents of rubidium 

 (Heier and Billings, 1970), but also of pegmatites 

 and evaporites, which are commonly enriched in 

 rubidium. According to Michael Fleischer (written 

 commun., 1972) the rubidium content of pegmatite 

 minerals is as much as 3.0 percent in microcline, 

 2.1 percent in muscovite, 4.1 percent in biotite, 4.5 

 percent in lepidolite, and 0.85 percent in pollucite; 

 minerals of the Tanco pegmatite reach or exceed 

 these maximums (Nickel, 1961, tables 1 and 4; Petr 

 Cerny, written commun., 1972). Among evaporite 

 minerals, the rubidium content is at most about 0.2 

 percent in sylvite and camallite (Michael Fleischer, 

 written commun., 1972). Because both sylvite and 

 carnallite are formed in the last stages of crystalli- 



